In many digital signals processing applications, such as digital communication systems, quadrature signals are utilized. Quadrature signals are formed by two components, referred to as I and Q signals, having the same frequency and amplitude, but which are 90° degrees out of phase, as shown in FIG. 1.
Frequently in digital communication systems a circuit or circuit element is connected to only one of the I and Q signals. In this case, the I and Q signals are loaded asymmetrically. For example, in a down-converter a phase locked loop (PLL) is connected to only the I signal. However, it is important to ensure that the quadrature relationship is maintained between the I and Q signals, that is, that they remain 90° degrees out of phase.
One solution to ensuring that the I and Q signals remain 90° degrees out of phase disclosed in US 2006/0091919 is to connect a dummy load to the one of the I and Q signals which is not connected to the circuit element. FIG. 2 shows a system including a divide by two circuit 110 which is arranged to output I and Q signals. The I signal is received by a further divide by two circuit 120, whilst the Q signal, in order to remain 90° out of phase with the I signal, is connected to a dummy load 130. However, the use of such a dummy load may affect a relative amplitude of the Q signal compared to the I signal, waste power and/or generate additional heat.
It is an object of embodiments of the invention to at least mitigate one or more of the problems of the, prior art.